Negative electrode active material for non-aqueous electrolyte secondary battery, non-aqueous electrolyte secondary battery using same, and method for producing negative electrode active material for non-aqueous electrolyte secondary battery

Abstract

The disclosed negative electrode active material for a nonaqueous electrolyte secondary battery includes active material particles containing silicon, and a surface layer formed on surfaces of the active material particles. The surface layer contains a reaction product of a compound allowed to react so as to form a siloxane bond. The compound includes a structure represented by Si-R1-Si. The R1 is an atomic group having a chain portion including, as constituent elements, an alkylene group and at least one selected from the group consisting of a sulfur atom, an oxygen atom, and a nitrogen atom. The two Si's are each bound with at least one atomic group selected from the group consisting of an alkoxy group having 1 to 6 carbon atoms, and the like.

1 . A negative electrode active material for a nonaqueous electrolyte secondary battery, comprising:
 active material particles containing silicon; and   a surface layer formed on surfaces of the active material particles, wherein   the surface layer contains a reaction product of a compound allowed to react so as to form a siloxane bond,   the compound includes a structure represented by Si-R1-Si,   the R1 is an atomic group having a chain portion including, as constituent elements, an alkylene group and at least one selected from the group consisting of a sulfur atom, an oxygen atom, and a nitrogen atom,   one of the two Si's is bound with at least one atomic group selected from the group consisting of an alkoxy group having 1 to 6 carbon atoms, a group including an oxyalkylene group and represented by —O—(C x1 H 2x1+1 O y1 ) where x1 is an integer of 2 to 6, and y1 is an integer of 1 to 3, a chloro group, and a hydroxyl group, and   the other one of the two Si's is bound with at least one atomic group selected from the group consisting of an alkoxy group having 1 to 6 carbon atoms, a group including an oxyalkylene group and represented by —O—(C x2 H 2x2+1 O y2 ) where x2 is an integer of 2 to 6, and y2 is an integer of 1 to 3, a chloro group, and a hydroxyl group.   
     
     
         2 . The negative electrode active material according to  claim 1 , wherein the compound is a compound represented by the following formula (1): 
       
         
           
           
               
               
           
         
         wherein in the formula (1), at least one selected from the group consisting of R2, R3, and R4 is each independently an alkoxy group having 1 to 6 carbon atoms, a group including an oxyalkylene group and represented by —O—(C x1 H 2x1+1 O y1 ) where x1 is an integer of 2 to 6, and y1 is an integer of 1 to 3, a chloro group, or a hydroxyl group; at least one selected from the group consisting of R5, R6, and R7 is each independently an alkoxy group having 1 to 6 carbon atoms, a group including an oxyalkylene group and represented by —O—(C x2 H 2x2+1 O y2 ) where x2 is an integer of 2 to 6, and y2 is an integer of 1 to 3, a chloro group, or a hydroxyl group; the rest of R2 to R7 are each independently a hydrocarbon group having 1 to 6 carbon atoms, a hydrogen atom, or a group represented by C x3 H 2x3+y3+1 N y3 O z3 S w3  where x3 is an integer of 1 to 6, and y3 is an integer of 0 to 3, z3 is an integer of 0 to 3, w3 is an integer of 0 to 3, and 1≤ y3+z3+w3; and R2 to R7 may be the same or different. 
       
     
     
         3 . The negative electrode active material according to  claim 2 , wherein in the formula (1), R2 to R7 are a methoxy group or an ethoxy group. 
     
     
         4 . The negative electrode active material according to  claim 1 , wherein
 the R1 includes at least one heteroatom selected from the group consisting of a sulfur atom, an oxygen atom, and a nitrogen atom, and two alkylene groups constituting the chain portion so as to sandwich the at least one heteroatom, and   the two alkylene groups each independently have 2 to 4 carbon atoms.   
     
     
         5 . The negative electrode active material according to  claim 1 , wherein the R1 is any one of —(CH 2 ) p S n (CH 2 ) q — (1≤n≤6, 2≤p≤4, and 2≤q≤4), —(CH 2 ) p O(CH 2 ) q — (2≤p≤4 and 2≤q≤4), —(CH 2 ) p O(CH 2 ) r O(CH 2 ) q — (2≤p≤4, 2≤q≤4, and 2≤r≤4), and —(CH 2 ) p NH(CH 2 ) q — (2≤p≤4 and 2≤q≤4), where n, p, q, and r are each a natural number. 
     
     
         6 . The negative electrode active material according to  claim 1 , wherein the surface layer contains a conductive carbon. 
     
     
         7 . The negative electrode active material according to  claim 1 , wherein the active material particles are composite particles containing a lithium silicate phase represented by Li x SiO y  where 0<x≤4 and 0<y≤4, and a silicon phase dispersed in the lithium silicate phase. 
     
     
         8 . The negative electrode active material according to  claim 7 , wherein the silicon phase has a crystallite size in the range of 1 nm to 1000 nm. 
     
     
         9 . The negative electrode active material according to  claim 1 , wherein the active material particles contain a carbon phase, and a silicon phase dispersed in the carbon phase. 
     
     
         10 . A nonaqueous electrolyte secondary battery, comprising:
 a positive electrode; a negative electrode; and a nonaqueous electrolyte, wherein   the negative electrode includes the negative electrode active material according to  claim 1 .   
     
     
         11 . A production method of a negative electrode active material for a nonaqueous electrolyte secondary battery, the production method comprising:
 a first step of bringing a compound or a liquid in which the compound is dissolved, into contact with active material particles containing silicon; and   a second step of allowing the compound to react so as to form a siloxane bond, while the compound or the liquid are in contact with the active material particles; wherein   the compound includes a structure represented by Si-R1-Si,   the R1 is an atomic group having a chain portion including, as constituent elements, an alkylene group and at least one selected from the group consisting of a sulfur atom, an oxygen atom, and a nitrogen atom,   one of the two Si's is bound with at least one atomic group selected from the group consisting of an alkoxy group having 1 to 6 carbon atoms, a group including an oxyalkylene group and represented by —O—(C x1 H 2x1+1 O y1 ) where x1 is an integer of 2 to 6, and y1 is an integer of 1 to 3, a chloro group, and a hydroxyl group, and   the other one of the two Si's is bound with at least one atomic group selected from the group consisting of an alkoxy group having 1 to 6 carbon atoms, a group including an oxyalkylene group and represented by —O—(C x2 H 2x2+1 O y2 ) where x2 is an integer of 2 to 6, and y2 is an integer of 1 to 3, a chloro group, and a hydroxyl group.   
     
     
         12 . The production method according to  claim 11 , wherein the compound is a compound represented by the following formula (1): 
       
         
           
           
               
               
           
         
         wherein in the formula (1), at least one selected from the group consisting of R2, R3, and R4 is each independently an alkoxy group having 1 to 6 carbon atoms, a group including an oxyalkylene group and represented by —O—(C x1 H 2x1+1 O y1 ) where x1 is an integer of 2 to 6, and y1 is an integer of 1 to 3, a chloro group, or a hydroxyl group; at least one selected from the group consisting of R5, R6, and R7 is each independently an alkoxy group having 1 to 6 carbon atoms, a group including an oxyalkylene group and represented by —O—(C x2 H 2x2+1 O y2 ) where x2 is an integer of 2 to 6, and y2 is an integer of 1 to 3, a chloro group, or a hydroxyl group; the rest of R2 to R7 are each independently a hydrocarbon group having 1 to 6 carbon atoms, a hydrogen atom, or a group represented by C x3 H 2x3+y3+1 N y3 O z3 S w3  where x3 is an integer of 1 to 6, and y3 is an integer of 0 to 3, z3 is an integer of 0 to 3, w3 is an integer of 0 to 3, and 1≤y3+z3+w3; and R2 to R7 may be the same or different.